Medical stents are generally flexible, tubular, expandable bodies formed of a plurality of interconnecting wires. The stents are used in a wide variety of medical applications, such as treatment of esophageal diseases or reinforcing constricted blood vessels or urinary tracts. The stent is usually placed into a constricted portion of a patient's body using a delivery system, e.g. a catheter.
When a medical stent is used for treatment of an esophageal disease, such as esophageal tumor or stricture, the stent is placed at the lesion within the esophagus to maintain the esophageal lumen open. If the tumor or stricture is located near the junction between the stomach and the esophagus, the esophageal stent is often implanted across the lower esophageal sphincter (i.e. the ring-like muscle that constricts and relaxes the esophagus as required by normal physiological functions). However, the implantation of a stent across the normally-closed esophageal sphincter may hold the sphincter open unintentionally and cause harmful gastric acid reflux from the stomach into the esophagus.
In order to reduce the gastric acid reflux, it has been proposed to use an anti-reflux valve with an esophageal stent. An example of esophageal stent with an anti-reflux valve is disclosed by Köcher et al. (“Esophageal Stent with Antireflux Valve for Tumors Involving the Cardia: Work in Progress,” JVIR 1998; 9:1007-1010). The anti-reflux valve of Köcher et al. is made of a pliable, soft polyurethane sleeve attached to the lower end of the stent. However, there are several problems associated with this type of stent. For example, the sleeve must be long enough to prevent the reflux and act as a barrier wall to defeat capillary flow of acid up the bore of the device. Since the sleeve must be long, greater deployment force and more complex delivery catheter designs are required. Typically, the length of the sleeve ranges from about 50 to 120 mm and requires extra length on the delivery system to envelope it in the “folded” condition prior to deployment. In addition, the sleeve may become twisted, tangled, or kinked, which may inhibit the passage of food into the stomach. The sleeve also may become reversed and pushed up into the esophagus during vomiting. In that case, it may be difficult for the sleeve to return to its properly functioning position.